[FFmpeg-devel] [PATCH] avutil/display: fix inverted doc

[Andreas Rheinhardt]

Andreas Rheinhardt:
> Zhao Zhili:
>> ---
>>  libavutil/display.h | 2 +-
>>  1 file changed, 1 insertion(+), 1 deletion(-)
>>
>> diff --git a/libavutil/display.h b/libavutil/display.h
>> index 515adad795..d87bf68425 100644
>> --- a/libavutil/display.h
>> +++ b/libavutil/display.h
>> @@ -88,7 +88,7 @@
>>  double av_display_rotation_get(const int32_t matrix[9]);
>>  
>>  /**
>> - * Initialize a transformation matrix describing a pure counterclockwise
>> + * Initialize a transformation matrix describing a pure clockwise
>>   * rotation by the specified angle (in degrees).
>>   *
>>   * @param matrix an allocated transformation matrix (will be fully overwritten
>>
> 
> If you look at the documentation, you will notice that the matrix
> returned from the function is supposed to be multiplied from the right
> to the coordinate (row) vector, not from the left to the coordinate
> (column) vector as is standard in linear algebra. This is tantamount to
> transposing the matrix which for rotation matrices means negating the
> degree. So this doxy is correct.
> Notice that last time I looked at this, I came to the conclusion that
> the whole H.2645 SEI parsing code uses it wrongly.
> 

Wait, there is another difference to ordinary linear algebra: The y axis
is directed downwards. Maybe you are right. Let me think this through...

- Andreas